The following background is provided simply as an aid in understanding the disclosed apparatus and method and is not admitted to describe or constitute prior art.
In large commercial or industrial buildings (e.g. facilities, plants, etc.), electricity costs for lighting can be more than half of the total energy budget. Consequently, considerable economic benefits can be obtained through more efficient lighting techniques. Lighting technologies improve in performance and efficiency over time such that many existing commercial buildings will eventually consider some form of lighting retrofit or redeployment. In many cases, fluorescent lighting is the most desirable technology from the standpoint of the quality and quantity of light generated per unit cost.
Existing commercial or industrial buildings vary widely in age, construction, and intended use; hence, the electric power sources used in any given plant may vary. Typically, lighting is provided through high intensity discharge lighting that runs on single phase 120 Volts-Alternating Current (VAC), 208 VAC, 240 VAC, 277 VAC, or 480 VAC. However, three phase power, often 480 VAC, is what is most common at many large industrial, commercial, or manufacturing sites in the U.S.
Fluorescent lamps provide one of the most efficient forms of lighting. The fluorescent lamps in a fluorescent light fixture are powered by a ballast that converts line voltages to a high frequency, high voltage output. The type of ballast in a particular fixture determines, for example, the power consumption and optimal type of lamp to be used in the fixture.
Ballasts for fluorescent light fixtures are typically designed to receive single phase electrical power at a voltage level of 120 VAC or 277 VAC. Where a facility has a 480/277 Wye setup, ballasts can be run directly from a leg of the Wye. However, in this case, a dedicated 277 V circuit must be wired from the transformer throughout the facility. Additionally, the dedicated circuit must be load balanced on the Wye. Alternatively, a transformer can be used to adjust a plant 480 VAC single phase voltage to the 277 VAC voltage suitable for a typical ballast. However, creating 277 VAC single phase voltage for a large plant involves expensive transformers, wiring a dedicated circuit, and careful load balancing.
For example, in a grounded 480V Wye system, a plant would typically create a dedicated single phase 277V circuit for lighting. A centralized 480/277 step-down transformer, the primary of which is wired to two legs of the Wye, is typically installed at the main distribution panel. The lighting fixtures in the plant are then wired to this 277V circuit. Three main challenges are introduced using this method. First, there is considerable energy loss at the large centralized transformer and line loss over the wiring. Second, a dedicated circuit is expensive to wire throughout a plant. Third, the load on the Wye circuit must be balanced. Lights, in aggregate, draw a considerable amount of power; therefore, good electrical design practice requires that the lighting load be equally apportioned amongst the three legs of the Wye. Optimizing balancing requires careful load planning, which is difficult in a plant, or often requires the expense of additional transformers. Hence, a need exists for efficient methods of directly powering fluorescent lamps from a three phase power source.
Additionally, the ballast is typically hard wired inside the fixture, making ballast failures much more costly to repair than, for example, a lamp failure; hence, there is a need for techniques that reduce ballast failures.
Accordingly, it would be desirable to provide a transformer wiring method and apparatus for fluorescent lighting that provides any one or more of these advantageous features.